Move Over MPG, It’s Time For CO2e per Mile

Kyle Richmond-Crosset

Fast, Pretty, and Green: The Rise of the Electric Vehicle

Americans are addicted to cars. In 2014, there were 797 cars in the United States for every 1,000 people (Toroyan, 2015). 86% percent of working Americans used a car to travel to work in 2013 (McKenzie, 2015). At the same time, Americans are beginning to recognize the human-caused danger of climate change. Gallup’s most recent public opinion poll shows that two-thirds of Americans are worried about global warming and believe that humans are the primary cause; these are sharp increases from years past (Saad, 2016). Despite this concern, Americans are still driving at similar rates to years past, which contributes significantly to climate change (Jaffe, 2015). The transportation sector produces 26% of the greenhouse gases emitted in the United States, and driving related emissions account for more than half of these emissions (“Sources of…,” 2016).

In order to balance an insatiable appetite for cars with increasing concern for the environment and climate change, Americans are buying more environmentally friendly vehicles. The rapid increase in market share of fuel efficient vehicles in the United States is stunning. The market share of hybrid electric vehicles (HEVs) among new car sales was 0.24% in 2002 and 2.21% in 2015, a nearly tenfold increase (Cobb, 2016). Among plug-in electric vehicles (PEVs), the market share of new car sales was 0.14% in 2011 (the first year PEVs were widely available) and 0.66% in 2015, a nearly fivefold increase in only 4 years (Cobb, 2016).

Automotive companies are responding to customer demand for fast, beautiful, and environmentally friendly vehicles by introducing new and improved PEV models. Tesla, which in 2015 had the “first IPO for an American car company since Ford went public in 1956,” has been successful entirely because they have fulfilled this demand (Urban, 2015). Before the Tesla Model X, a beautiful, fast vehicle meant very low fuel economy, and fuel efficient vehicles like the Prius were slower and decidedly not sleek. Tesla’s ability to break into the market hinges upon its claim that not only is a Tesla good-looking and powerful, but good for the environment as well.

For more than 130 years, automobiles have been powered by internal combustion engines running on some type of fossil fuel (Urban, 2015). The Tesla Model 3, along with the many other PEVs entering the market in the next few years, are the first mainstream, popular, and commercially viable vehicles in the history of the car with no internal combustion engine. This is a radical departure from the past.

Fuel Efficiency: MPG and MPGe

In order to accurately compare the environmental friendliness of vehicles with internal combustion engines (gasoline vehicles) and PEVs, it is necessary to develop measurements that are up to the task. Currently, the most common way of evaluating a car’s impact on the environment is a measurement of how many miles the vehicle can travel on one gallon of gasoline, or its MPG. This standard of fuel efficiency works fine for gasoline vehicles but cannot accurately measure PEVs; in a Tesla, there are no gallons of gas or of any other fuel. The Environmental Protection Agency (EPA) developed a miles per gallon equivalent (MPGe) unit of measurement that accommodates all types of vehicles (“New Fuel…,” 2010). Using MPGe, it is clear that electric vehicles are the most fuel efficient. The average fuel economy of new vehicles sold in 2016 is 25.1 MPGe, while the average fuel economy for new PEVs sold in 2016 is 104 MPGe (Gareffa, 2016).

The introduction of PEVs into the automotive sector has exposed a limitation of MPG: it is a unit of measurement built to measure the fuel efficiency of internal combustion engines only. For PEVs, MPGe relies on a series of conversions that translate electricity into gallons of fuel. This provides a usable workaround and is the standard measurement of fuel efficiency across all vehicles.

Unfortunately, consumers have used MPG (and now MPGe) not only as a measurement of fuel efficiency but also as a proxy for environmental friendliness and greenhouse gas emissions. This assumption was reasonable until the introduction of PEVs. Gasoline vehicles all use the same fuel, so the environmental issues with extraction, refinement, and transportation of the fuel are essentially equivalent regardless of the vehicle. Therefore, the disparity in greenhouse gas emissions between vehicles is almost entirely dependent on its fuel efficiency, of which MPG is the standard unit of measurement. PEVs ruin this assumption, because the greenhouse gas emissions related to the production of electricity are very different than the emissions related to the production of gasoline.

Greenhouse Gas Emissions: MPGghg

In order to directly compare the greenhouse gas emissions of PEVs and gasoline vehicles, the Union of Concerned Scientists have developed MPGghg (Nealer, 2015). This unit of measurement calculates the amount of greenhouse gases that are emitted during the production and use of the electricity needed to power a PEV for one mile (Nealer, 2015). In the interest of simplicity, the MPGghg of a PEV is directly comparable to the MPG of a gasoline vehicle. In other words, a electric car that gets 27 MPGghg produces the same amount of greenhouse gases per mile as a gasoline powered car that gets 27 MPG.

The Union of Concerned Scientists explains their methodology as follows: “In comparing EVs’ global warming emissions with gasoline vehicles’ emissions, we take a ‘well-to-wheels’ approach that accounts for the full fuel cycle for both types of vehicles” (Nealer, 2015). This measurement therefore depends significantly on the sources of electricity for electric vehicles. For example, 2012 data in Michigan shows that the average PEV gets 39 MPGghg (Nealer, 2015). That is, any gasoline vehicle with a fuel economy of greater than 39 MPG in Michigan would produce less greenhouse gases per mile than an average PEV charged in the state. However, New York produces a significant portion of its electricity from renewable sources, so the average PEV gets 135 MPGghg (Nealer, 2015). On average, an EV vehicle in the United States emits the equivalent greenhouse gases of a gasoline vehicle that gets 68 MPG (Nealer, 2015).

One significant advantage to PEVs is that as electric grids get more energy from renewable sources, the environmental impact per mile of the vehicles decline. Theoretically, a PEV charged on an electrical grid powered entirely by renewable energy could have almost no greenhouse gas emissions per mile. In gasoline vehicles, fuel efficiency is the only way to reduce emissions because the fuel source itself is not replaceable. Per mile, PEVs already emit fewer greenhouse gases than gasoline vehicles, and this disparity is increasing as electric grids use more renewable energy sources (Nealer, 2015).

Life-Cycle Assessment: CO2e per Mile

MPGghg effectively calculates greenhouse gas emissions related to fuel production and use, but this measure neglects the potential global warming impact of the manufacturing process of the car itself. PEVs have a significantly different manufacturing process because of their large batteries. For example, the battery in the Tesla Model S weighs more than 1,300 pounds and is composed partially of lithium, a metal costly and difficult to extract (“Tesla…, 2014). As a result, the greenhouse gas emissions related to the manufacturing of a full-size PEV are more than two-thirds higher than the corresponding emissions of a gasoline vehicle (Nealer, 2015). However, the higher emissions of greenhouse gases when manufacturing an PEV are offset by lower emissions per mile once the PEV is on the road. On average in the United States, the mileage at which greenhouse gas emissions (measured using carbon dioxide equivalent, or CO2e) from a comparable PEV and gasoline vehicle are equivalent is 4,900 miles, or about six months (Nealer, 2015). After that, the PEV will produce less combined CO2e.

The most complete measurement of greenhouse gas emissions is CO2e per mile. This measurement includes emissions related to the manufacturing process of the car, the production and use of the fuel during the average lifetime of the car, and the disposal of the car (Nealer, 2015). The total amount of emissions is converted to CO2e and divided by the expected lifetime mileage of the car. CO2e per mile works equally well on PEVs and gasoline vehicles, and uses a holistic approach to measuring environmental impact.

A Fundamental Shift

As Americans indicate their desire for fuel efficient, environmentally friendly PEVs, it is important that there is also a fundamental shift in how we measure fuel efficiency and environmental impact. MPG is suited for a world without PEVs; its continued relevance is due to ubiquity, not usefulness. While MPGe has emerged as an effective way to measure fuel efficiency across all vehicles, it is not useful as a measurement of greenhouse gas emissions. MPGghg does an imperfect job, but fails to include the environmental costs of the manufacturing process of the car. Ultimately, CO2e per mile is the all-inclusive environmental indicator, but it is also the most complicated to calculate and conceptualize. This may be why CO2e per mile is not yet a standard unit of measurement in the automotive industry.

Electric vehicles have jolted the automotive market, and the standard measurements of environmental impact are no longer adequate. Americans who want to purchase a vehicle today are faced with confusing and incomplete metrics. Accurate and helpful units of measurement do not appear on car labels out of thin air; it is essential that government regulators and automotive companies work together to ensure that Americans understand the environmental impact of the vehicles they are buying. The adoption of CO2e per mile as the standard environmental impact unit of measurement would go a long way towards that goal.

Works Cited

Cobb, Jeff. "December 2015 Dashboard." HybridCars, 3 Jan. 2016. Web. 03 Nov. 2016.

Gareffa, Peter. "Average Fuel Economy for New Vehicles Jumps to 25.1 MPG in January." Edmunds, 04 Feb. 2016. Web. 04 Nov. 2016.

Jaffe, Eric. "Driving in America Is Approaching a 'New Normal'" CityLab. The Atlantic, 23 Mar. 2015. Web. 03 Nov. 2016.

McKenzie, Brian. "Who Drives to Work? Commuting by Automobile in the United States: 2013." American Community Survey Reports (2015): n. pag. U.S Census Bureau, Aug. 2015. Web. 3 Nov. 2016.

Nealer, Rachael, David Reichmuth, and Don Anair. "Cleaner Cars from Cradle to Grave." (2015): n. pag. Union of Concerned Scientists. Union of Concerned Scientists, Nov. 2015. Web. 4 Nov. 2016.

New Fuel Economy and Environment Labels for a New Generation of Vehicles. N.p.: Environmental Protection Agency, Nov. 2010. PDF.

Saad, Lydia, and Jeffrey M. Jones. "U.S. Concern About Global Warming at Eight-Year High." Gallup, 16 Mar. 2016. Web. 03 Nov. 2016.

"Sources of Greenhouse Gas Emissions." EPA. Environmental Protection Agency, 6 Oct. 2016. Web. 03 Nov. 2016.

"Tesla Model S Weight Distribution." Teslarati, 02 July 2014. Web. 04 Nov. 2016.

Toroyan, Tami. Global Status Report on Road Safety. Geneva: World Health Organization, 2015. PDF.

Urban, Tim. "How Tesla Will Change The World." Wait But Why. WaitButWhy, 02 June 2015. Web. 03 Nov. 2016.

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last updated 9/19/16